Method of manufacturing curved gas discharge lamps



Dec. 20, 1966 L. E. VRENKEN ETAL METHOD OF MANUFACTURING CURVED GAS DISCHARGE LAMPS Filed July 30, 1965 LOUIS E. VRENKEN ADRIANUS J.TH. MOLLET QAM/a AGE/vr 2 Sheets-Sheet 2 L. E. VRENKEN ETAL METHOD OF MANUFACTURING CURVED GAS DISCHARGE LAMPS Filed July 30, 1963 Dec. 20, 1966 INVENTOR. LOUIS E. VRENKEN ADRIANUS J.TH. MOLLET BY i f.

A@ E N T United States Patent O 3,292,937 METHOD F MANUFACTURING CURVED GAS DISCHARGE LAMPS Louis Eugene Vrenken and Adrianus Josephus Theresia Mollet, Emmasingel, Eindhoven, Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed July 30, 1963, Ser. No. 298,567 Claims priority, application Netherlands, Sept. S, 1962,

282,921 Claims. (Cl. S16- 21) The invention relates to a method of manufacturing a curved gas discharge lamp in which the gas pressure at room temperature is lower than the atmospheric pressure, particularly to a method of manufacturing a circularly curved low-pressure mercury vapor discharge lamp, and to discharge lamps manufactured by such a method.

The manufacture of curved gas discharge lamps, particularly of circularly curved gas discharge lamps, always starts with a straight glass tube which, after being heated to the required temperature, is shaped into the desired curved form. As is the case in the manufacture of similar straight gas discharge lamps, the initial straight glass tube is provided at both ends with a closure member, mostly a glass bottom, connected in a gas-tight manner with the wall of the tube. In at least one of these members provision is made of an opening through which the interior of the tube communicates with the space outside the tube. This opening, which generally is in the form of a glass exhaust tube is necessary to remove undesired gases from the tube during the manufacture of the lamp and to introduce desired filling gases into the tube. In the conventional methods of manufacturing curved lamps, the curved tube is subjected to a pumping process in which the gases undesirable for a lamp including the gases evolved from the glass wall and the electrodes during their process are removed from the curved tube during a heat treatment; the desired gas filling may then be introduced into the tube.

In order to accelerate the removal of the undesirable gases, it is usual both in the manufacture of straight and of curved mercury vapour discharge lamps in which only one opening is available during the pumping process, to use a so-called mercury flush during the pumping process. After the pressure in the tube has been brought to a given value by means of pumping, a controlled amount of liquid mercury is introduced into the tube. With straight tubes suspended vertically and having the opening at the upper end, the mercury drops as far as the closed end of the tube where it vaporizes very rapidly, as a result of which, so to say, a piston of mercury vapor pushes the undesirable gases from the hot tube upwardly to the opening, which results in a strong reduction of the partial pressures of the undesirable gases in the tube. In tubes which have been curved already the mercury flush is considerably less effective, since it is impossible to bring the mercury to be vaporized close to the closed end of the tube in a simple manner. The mercury introduced is consequently always deposited at a point between the open end and the closed end of the tube. Thus, during the vaporization of the mercury, part of the undesirable gas filling is pushed towards the closed end of the tube from which it can be removed practically only by a prolonged pumping process, so that the advantages of the use of a mercury fiush are substantially not obtained. As a result of the poor effect of the mercury ilush in curved lamps, the finished lamp exhibits a smaller light output and a more rapid decrease in the quantity of emitted radiation.

After the tube has been treated in the manner described hereinbefore, it is filled with the desired gas or gas mix- 3,292,987 Patented Dec. 20, 1966 ICC ture. In case of a low-pressure mercury vapor discharge lamp, this filling may consist, for example, of mercury vapor and a rare gas or a mixture of rare gases. The mercury vapor is formed by the introduced, the so-called dosage, of a particular quantity of mercury, for which purpose a special dosing device is used.

If a tube used either for the manufacture of straight gas discharge lamps or for the manufacture of curved, for example, circularly curved gas discharge lamps, has an opening at either end, it is also possible to make use of the mercury flush, but alternatively a so-called rinsing process may be used. In this rinsing process, an inert gas, for example nitrogen, is introduced into the tube through one opening, while a pumping process is carried out at the other end of the tube. Consequently, in this process the undesirable gases, mixed with the inert rinsing gas, are removed by rinsing. The rinsing treatment with the inert rinsing gas is followed after some time by a rinsing treatment with the rare gas or gas mixture which is needed in the lamp later. After the termination of the rinsing treatment, the pressure in the tube is reduced by pumping to the desired final value; if required, for example, in case of a low-pressure mercury vapor discharge lamp, an additional controlled quantity of mercury is introduced. Thus the final filling can readily be obtained.

Both in the method using a mercury fiush and in that using the rinsing process, the manufacture is effected most eicaciously at the highest possible temperature of the lamp. Preferably, this temperature is chosen just below the softening temperature of the glass of the tube. In the manufacture of straight lamps, the temperature can actually be raised during the pumping process to a value just below the softening temperature. In the manufacture of curved lamps, in particular of circularly curved low-pressure mercury vapor discharge lamps, in which the tube has already been shaped into the desired form prior to the pumping process, the temperature cannot be raised to so high a value during the pumping process, since at too high a temperature deformation of the tube will soon occur.

A method in accordance with the invention for the manufacture of a curved gas discharge lamp, in which the gas pressure at room temperature is lower than the atmospheric pressure, which method consists in that a straight glass tube provided at both ends with a closure member connected in a gas-tight manner to the wall of the tube is bent in the hot state, atleast one of these members having an opening through which the interior of the tube communicates with the space outside the tube, which straight tube is subjected to a heat treatment during which undesirable gases are removed from the interior of the tube, is characterized in that during the last phase of the heat treatment, so great a quantity of rare gas is introduced into the tube that the pressure in this tube becomes substantially equal to the atmospheric pressure, after which the tube is bent and then is pumped to the desired pressure and, if desired, filled with other filling constituents, for example, mercury or sodium, and finally closed.

The fundamental difference from the known method brieiiy described hereinbefore consists in that according to the invention the straight glass tube is bent after almost all the operations required to convert the tube into a discharge lamp have already been carried out. The important advantage thus obtained consists in that the heat treatment can now be effected at a temperature lying just below the softening point of the glass tube; consequently, the heat treatment is now as effective for curved lamps as for straight lamps. This advantage holds both for the method in which a mercury iiush is used and for the method using a rinsing process.

When use is made of a mercury flush, an additional advantage is obtained. Since the tube is still straight during the introduction of the mercury and is preferably arranged in a vertical position, the liquid mercury can be brought near the closed end; the mercury vapor formed then sweeps all the undesirable gases towards the open end of the tube.

Since the straight tube, prior to being bent, is lled with an inert gas, for example, nitrogen or rare gas, to a pressure approximately equal to atmospheric pressure, substantially no deformation of the tube occurs during the bending process.

The invention will now be described more fully with reference to the accompanying drawing, which shows diagrammatically both a known method of manufacturing low-pressure mercury vapor discharge lamps and a method in accordance with the invention.

FIG.1 shows the known method of manufacturing, in which a mercury flush is used;

FIG. 2 illustrates the method of manufacturing in accordance with the invention, in which a mercury flush is used;

FIG. 3 shows the method in accordance with the invention in which use is made of a rinsing process.

All figures also show graphically the temperature variation during the manufacture. As a matter of course, this temperature variation is shown schematically, since some stages of the manufacture are of longer duration than others. Hence, the unit of time plotted on the abscissa of the graph is not constant. Furthermore, a broken line is drawn in the graph parallel to the abscissa through the point on the ordinate designating the value of the softening temperature of the glass of the tube. As is clearly evident from a comparison of FIG. 1 with FIGS. 2 and 3, respectively, in a method in accordance with the invention the heat treatment during the pumping process is effected at a temperature which lies much closer to the softening temperature of the glass than in case of the use of the known method (FIG. 1).

When use is made of a mercury flush according to FIGS. 1 and 2, the tubes have only one opening during the pumping process. This opening, for example, an exhaust tube, is closed at the moment indicated by the arrows 1 and 2, respectively.

When the rinsing process according to FIG. 3 is used, the tube has two openings. The first opening must be closed after the introduction of the rare gas. This moment precedes the bending process and is indicated by the arrow 3. After the tube has been completely finished, the second opening must obviously be closed, which is indicated by the arrow 4.

As is known, the electrodes must be fired during the manufacture. In the method shown, this may be effected during the time intervals indicated in FIGS. 1, 2 and 3.

What is claimed is:

1. A method of manufacturing a curved gas discharge lamp comprising evacuating a tubular envelope hermetically sealed at both ends by members one of which is provided with a channel connecting the interior of the envelope to the exterior thereof, heating said tubular envelope to remove undesirable gases within the interior of the envelope through said channel, introducing a quantity of inert gas into the envelope through said channel to increase the pressure within said envelope to about 1 atmosphere while said envelope is heated, bending the envelope into a curved shape, evacuating the gas within said envelope to reduce the pressure thereof to a desired value, introducing an ionizable medium into the envelope, and closing said channel to seal said envelope.

2. A method of manufacturing a curved gas discharge lamp comprising evacuating a tubular envelope hermetically sealed at both ends by members one of which is t provided with a channel connecting the interior of the envelope to the exterior thereof, heating said tubular envelope, introducing mercury into the envelope to remove undesirable gases within the interior `of the envelope:Y

through said channel, introducing a quantity of inert gas ,into the envelope through said channel to increase the pressure within said envelope to about 1 atmosphere while said envelopek is heated, bending the envelope into a curved shape, evacuating the gas within said envelope to reduce the pressure thereof to a desired value, introducing an ionizable medium into the envelope, and closing said channel to seal said envelope.

3. A method of manufacturing a curved gas discharge lamp comprising evacuating a tubular envelope hermetically sealed at both ends by members which are each provided with a channel connecting the interior of thel envelope to the exterior/thereof, heating said tubularthe envelope to increase the pressure within said envelope i to about 1 atmosphere while said envelope is heated, bending the envelope into a curved shape, evacuating the gas within said envelope to reduce the pressure thereof i to a desired value, introducing an ionizable medium into the envelope, and closing said channel to `seal said envelope. l

4. A method of manufacturing a curved gas discharge i lamp comprising evacuating a tubular envelope hermetically sealed at both ends by members one of which is provided with a channel connecting the interior of the i envelope to the exterior thereof, heating said tubular en-` velope to remove undesirable gases within the interior of the envelope through said channel, introducing a quantity of inert gas into the envelope through said channel to increase the pressure within said envelope to about 1 atmosphere while said envelope is heated, bending the envelope into a curved shape, evacuating the gas within said envelope to reduce the pressure thereof to a desired value, introducing a quantity of mercury sufficient to maintain a discharge into the envelope, and closing said channel to seal said envelope.`

5. A method of manufacturing a curved gas discharge lamp comprising evacuating a tubular envelope herme-A tically sealed at both ends by members one of which is provided with a channel connectingthe interior of the envelope to the exterior thereof, heating said tubular envelope to remove undesirable gases within the interior of the envelope through said channel, introducing a quantity of inert gasinto the envelope through said channel to` increase the pressure within said envelope to about 1 atmosphere while said envelope is heated, bending the envelope into a curved shape, evacuating the gas within said envelope to reduce the pressure thereof to a desired value, introducing a quantity of sodium sufficient to maintain a discharge into the envelope, and closing said channel to seal said envelope.

References Cited by the Examiner UNITED STATES PATENTS 2,454,745 11/1948 Quinn E g., l316---17 FRANK E. BAILEY, Primary Examiner. 

1. A METHOD OF MANUFACTURING A CURVED GAS DISCHARGE LAMP COMPRISING EVACUATING A TUBULAR ENVELOPE HERMETICALLY SEALED AT BOTH ENDS BY MEMBERS ONE OF WHICH IS PROVIDED WITH A CHANNEL CONNECTING THE INTERIOR OF THE ENVELOPE TO THE EXTERIOR THEREOF, HEATING SAID TUBULAR ENVELOPE TO REMOVE UNDERSIRABLE GASES WITHIN THE INTERIOR OF THE ENVELOPE THROUGH SAID CHANNEL, INTRODUCING A QUANTITY OF INERT GAS INTO THE ENVELOPE THROUGH SAID CHANNEL TO INCREASE THE PRESSURE WITHIN SAID ENVELOPE TO ABOUT 1 ATMOSPHERE WHILE SAID ENVELOPE IS HEATED, BEINDING THE ENVELOPE INTO A CURVED SHAPE, EVACUATING THE GAS WITHIN 